Autodeposition has been in commercial use on steel for about thirty years and is now well established for that use. For details, see for example, U.S. Pat. Nos. 3,063,877; 3,585,084; 3,592,699; 3,674,567; 3,791,431; 3,795,546; 4,030,945; 4,108,817; 4,178,400; 4,186,226; 4,242,379; 4,234,704; 4,636,264; 4,636,265; 4,800,106; and 5,342,694. The disclosures of all these patents are hereby incorporated by reference. Epoxy resin-based autodeposition coating systems are described in U.S. Pat. No. 4,180,603 (Howell. Jr.); U.S. Pat. No. 4,289,826 (Howell Jr.); U.S. Pat. No. 5,500,460 (Ahmed et al.); U.S. Pat. No. 6,096,806 (Mueller et al.) and International Publication Number WO 00/71337, the teachings of each of which are incorporated by reference.
Autodeposition compositions are usually in the form of a liquid, usually aqueous solutions, emulsions or dispersions in which active metal surfaces of inserted objects are coated with an adherent resin or polymer film that increases in thickness the longer the metal remains in the bath, even though the liquid is stable for a long time against spontaneous precipitation or flocculation of any resin or polymer, in the absence of contact with the active metal. When used in the autodeposition process, the composition when cured forms a polymeric coating. “Active metal” is defined as metal that spontaneously begins to dissolve at a substantial rate when introduced into the liquid solution or dispersion. Such compositions, and processes of forming a coating on a metal surface using such compositions, are commonly denoted in the art, and in this specification, as “autodeposition” or “autodepositing” compositions, dispersions, emulsions, suspensions, baths, solutions, processes, methods or a like term. Autodeposition is often contrasted with electrodeposition. Although each can produce adherent films with similar performance characterisitics, the dispersions from which they are produced and the mechanism by which they deposit are distinctly different. Electrodeposition requires that metal or other objects to be coated be connected to a source of direct current electricity for coating to occur. No such external electric current is used in autodeposition.
Prior epoxy emulsions used for autodeposition application are generally made by blending an epoxy functional resin(s) in a solvent. The epoxy resin may be blended with other coating components and additives such as crosslinking agents and/or coalescing solvents. The resulting solvent solution is then emulsified, with surfactants, in water and stripped of solvent to give a dispersion of resinous particles dispersed in water. This dispersion may then be used as a component of a coating bath. The dispersion, when autodeposited on a metal surface and cured, forms a polymeric coating.
All previous epoxy-coating compositions have relied on an emulsifier(s), usually in the form of external surfactant(s), to form stable emulsions of resinous particles in water. Epoxy coating compositions based on this approach are expensive to manufacture because of the amount of solvent used and time required to strip the emulsified material. Large amounts of external surfactants can also lead to deleterious effects in the cured coating caused by the ionic character of small surfactant molecules and due to the ability of the surfactant molecules to migrate in the coating.
Thus, there is a need in the art for high solids, epoxy-based autophoretic coating materials that reduce or minimize the need for process solvents that adversely affect manufacturing costs. There is also a need in the art for a means to obtain the high solids, epoxy-based autodepositing coating materials that eliminate and/or minimize the need for external emulsifier, thereby eliminating or reducing the deleterious effects in the cured coating caused by the ionic character of small surfactant molecules and due to the ability of the surfactant molecules to migrate in the coating.